The present invention generally relates to an improved device for cooling ultrasonic horns of the type utilized to bond a web of textile material by ultrasonic bonding techniques. More particularly, the cooling device according to the present invention operates so as to cool the bonding horns at or above the nodal area thereof (e.g. the area of zero amplitude) so that heat naturally generated at the nodal area in addition to heat radiated from the fabric and conducted through the horn is counteracted to prevent deleterious effects of extreme temperature elevation.
Ultrasonic bonding techniques are particularly advantageous when processing non-woven webs of textile material and particularly heat joinable textile material such as synthetic fibers of a thermoplastic material. According to ultrasonic bonding technology, a bonding tool conventionally known in the art as a "bonding horn" is vibrated in the ultrasonic frequency range and is closely positioned with respect to the moving web of textile material. The bonding horn typically defines a surface (hereafter bonding surface) positioned in close proximity to, and in direct contact with the web to be bonded. Conventional means are provided so as to impart vibatory motion in the ultrasonic frequency range to the horn and thus ultrasonic frequency waves are transmitted to the surface of the textile web.
Those in the art will appreciate that proper positioning of the bonding horn is extremely important for the proper functioning thereof in accordance with ultrasonic bonding techniques. For example, the conventional bonding horn at its bonding surface will exhibit vibratory movement of maximum amplitude while the other end of the bonding horn exhibits another area of maximum amplitude. However, intermediate the two ends of the bonding horn there is an area of substantially zero amplitude conventionally referred to as the "node" or "nodal area". The areas of maximum amplitude on the other hand are commonly referred to as "anti-nodes" or "antinodal areas". This terminology will be used hereinafter as these are art-recognized terms for bonding horn behavior.
As the bonding horn vibrates, energy in the form of ultrasonic frequency waves is transmitted to the moving web of textile material. It is desirable that such frequency waves contact the web at maximum amplitude thereof so that vibrations can be imparted to the individual fibers in the textile web. Such vibrations, of course, produce movement of the individual fibers in the textile web and, in the area where these fibers contact one another, frictional forces generate heat to a sufficient degree so that at such points of contact, individual fibers will become somewhat melted. Upon cooling, these fibers are thus securely bonded to one another.
The temperature of the bonding horn exhibits a pronounced effect upon the ability of the horn to perform its intended function. For example, when the temperature of the bonding horn exceeds a certain predetermined value, thermal expansion thereof may adversely effect the bonding horn's natural resonant frequency thereby deleteriously affecting the quality of the bond imparted to the textile web. Moreover, since most horns are solid structures, heat generated at the bonding surface/textile web interface can be conducted up through the horn and thereby adversely affect the electronic converter normally associated with conventional bonding horns which converts electrical oscillations to mechanical oscillations. It is known that heat will naturally be generated in the nodal area of the bonding horns by virtue of the ultrasonic frequency operation thereof and that the heat thus generated can also deleteriously affect the proper operation of the bonding horn.
It is therefore important that bonding horns in any ultrasonic bonding apparatus be maintained at a proper predetermined temperature or, that the heat generated during the bonding operation be counteracted by suitable cooling means.
One prior art proposal for solving the problems inherent in utilizing ultrasonic bonding techniques is evidenced by reference to U.S. Pat. No. 3,405,024 to Attwood et al. Attwood et al disclose that a heater can be utilized so as to maintain the bonding horn at a proper predetermined temperature. In this regard, there is described in this prior art patent, a cyclical operation of the heater so that the temperature of the bonding horn can be maintained within a predetermined set range. Attwood et al utilize "spot" cooling wherein air is directed in an impinging relationship onto the surface of a conical bonding horn in the area between the horns bonding surface and the nodal point. Thus, when employing the system of Attwood et al, the heat generated at nodal area of the bonding horn remains unchecked.
While Attwood et al is certainly appropriate for use in a single bonding horn application, in today's modern textile mill wherein a substantially continuously moving web is desired to be ultrasonically bonded across the entire width thereof, such an apparatus suffers from some significant defects. For example, entire width ultrasonic bonding normally utilizes a plurality of bonding horns which are elongated in the width dimensions. Such horns are disposed in either a straight line or in a staggered relationship across the entire width of a substantially continuously moving textile web. Due to the elongation of the bonding horns, spot cooling as suggested by Attwood et al would have the deleterious effect of producing an irregular temperature distribution profile on the horn's surfaces. This, of course, is undesirable as any non-uniformity of horn temperature can lead to improper horn functioning. Moreover, by having the cooling air impringe upon the surface of the bonding horn between the node and the bonding surface thereof, the heat generated at the node is ignored when utilizing the system of Attwood et al thereby promoting temperature distortion in the horn.
It has been surprisingly discovered, however, that a narrow band of cooling fluid (e.g. air) preferably directed against both side surfaces of an elongated horn at or above the nodal area thereof can be effective in counteracting both types of heat generated during ultrasonic bonding techniques. For example, according to the present invention there is provided an apparatus which includes a manifold which is elongated in the transverse machine direction and closely disposed relative to each of the plurality of elongated bonding horns so as to permit the air flowing therethrough to impinge directly upon both side surfaces of the bonding horns at or above the node area thereof. In such a manner, heat radiated from the surface of the moving web due to ultrasonic bonding and conducted through the horn as well as heat naturally generated during vibratory movement of the horn at the node can be controlled and counteracted. Thus such heat will not deleteriously affect the electronic equipment which imparts vibratory movement to the bonding horn.
These and other advantages and aspects of the present invention will become more aparent after careful consideration is given to the detailed description of the preferred exemplary embodiment which follows.